(A) Field of the Invention
The present invention relates to an apparatus and a method for detecting surface plasmon resonance (SPR). More particularly, the present invention relates to an image-phase apparatus and a method for detecting the SPR.
(B) Description of the Prior Art
The physical characteristics will change slightly while there are inter biomolecules interactions happening on the surface of bio-thinfilm. If such tiny physical change can be detected by certain means of technique, the techniques became a method of analyzing biomolecular interactions.
With the development and combination of optical technology and Micro-Electro-Mechanical Systems (MEMS), various biosensing technologies have been developed, for example, Confocal Laser Scanning Fluorescence microscopy (CLSFM), Quartz Crystal Micro-balance (QCM), Surface Plasmon Resonance (SPR), etc. Among them, SPR technology has the highest sensitivity of interfacial bio-interactions.
Since B. Liedberg applied the SPR principle to detect air composition in 1983, analyzers based on SPR have been widely and successfully applied in various research fields. For example, SPR technology and biochips are combined for the application of biomedical detection, in which it is not necessary to use the fluorescent labeling. Moreover, it can detect fast detection and has high sensitivity, and can replace the fluorescent labeling method in certain applications.
According to the working principle, SPR technology is usually classified into the following categories: (1) Detection of resonant angle by angle modulation; (2) Detection of a resonant wavelength by a light wavelength modulation; (3) Intensity detection; and (4) Phase-sensing. According to prior research papers, the resolution for angle modulation or light wavelength modulation to the refractive index is approximately 10−5 refractive index unit (RIU), and the resolution for the phase-sensing is higher, which approached up to 10−7 RIU. The angle modulation method or the light wavelength modulation method is simple and is used in most of the current SPR instruments. However, as the concentration of the sample to be detected is becoming lower and lower and users generally demanding for higher resolution, phase detection method with a high resolution has become the current trend for technical development. On the other hand, fast detecting and filtering are the future trend for biomolecular sensing, and full-field imaging analysis is also one of the crucial points in the development.
U.S. Patent Application No. 2003/0219809, filed by Chen Shean-Jen et al., discloses a PZT phase-shifting method used in obtaining the phase difference of the SPR phenomenon, and the system architecture is an SPR detecting apparatus 10, as shown in FIG. 1. A light beam emitted by a laser light source 11 is split into two lights through a polarizing plate 12 and a light beam amplifier 13, and the two lights are incident into a prism 14, and a reflection occurs on a surface of a metal film 15 adjacent to the prism 14. The two reflection lights emit to a light-emitting diode (LED) 18 through beam splitters 16, 17 and a lens 21. In addition, the reflection light is split into another two lights towards a PZT driving element 19 through the beam splitter 16, and then received by a charge-coupled device (CCD) 22 through a ½ wave plate 23, a beam splitter 20, and another lens 21. Then, according to an optical signal received by the CCD device 22, a mathematical operation is used to obtain phase differences of the object to be detected. The disadvantage of this method lies in the fact that the price of the current PZT driving element is relatively high, and a high voltage power source is required for the PZT element, so the cost of the instrument will increase.
Furthermore, for the current SPR phase-detecting technologies, a heterodyne light source together with a lock-in amplifier is mostly used to obtain the phase, or a piezoelectric actuator together with a five-step phase-shifting method is used to obtain the phase. For the above two processes, the fabricating method is complex and the building cost for the instrument is relatively high. In addition, as to the five-step phase-shifting method, it is necessary to take five images to calculate a set of meaningful data, so sampling time is relatively long.